Zika virus, a flavivirus classified within the Flaviviridae with other important mosquito-borne viruses, including yellow fever, dengue, West Nile and Japanese encephalitis viruses, has spread rapidly in a hemispheric-wide epidemic since the virus was introduced to Brazil in 2015, reaching Central and North Americas, including territories of the United States and now threatening the continental U.S. Initially isolated in 1947 in Uganda, the virus was first linked to human disease in 1952 and has been recognized sporadically as a cause of mild, self-limited febrile illness in Africa and Southeast Asia (Weaver et al., Antiviral Res 130:69-80, 2016; Faria et al., Science 352(6283):345-349, 2016). However, in 2007, an outbreak appeared in the North Pacific island of Yap, transferred there presumably from Asia, and subsequently disseminated from island to island across the Pacific, leading to an extensive outbreak in 2013-2014 in French Polynesia, with subsequent spread to New Caledonia, the Cook Islands, and ultimately to Easter Island, far to the East. An Asian lineage virus subsequently was transferred to the Western Hemisphere by routes that remain undetermined (Faria et al., Science 352(6283):345-349, 2016). The virus is transmitted anthropontically by Aedes aegypti, A. albopictus and possibly A. hensilli and A. polynieseinsis (Weaver et al., Antiviral Res 130:69-80, 2016).
In late 2015, a significant increase in fetal abnormalities (e.g. microcephaly) and Guillain-Barré syndrome (GBS) in areas of widespread Zika virus infection raised concerns that Zika virus might be much more virulent than originally thought and prompted the World Health Organization (WHO) to declare a Public Health Emergency of International Concern (PHEIC) (Heymann et al., Lancet 387(10020):719-721, 2016).